Apparatus and method for eliminating gases from a thermometer blank



July 22, 1969 w. A. AYRES 3,456,487

APPARATUS AND METHOD won ELJIMINA'IING GASES FROM A 'IHI-IRMOME'IER BLANK Filed March 4, 1968 I2 Sheets-Sheet 1 INVENTOR. WAL DM4 A 4/25;

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United States Patent Ot'fice 3,456,487 Patented July 22, 1969 3,456,487 APPARATUS AND METHOD FOR ELIMINATING GASES FROM A THERMOMETER BLANK Waldemar A. Ayres, Rutherford, N.J., assignor to Becton,

Dickinson and Company, East Rutherford, N.J., a corporation of New Jersey Continuation-in-part of application Ser. No. 548,224, May 6, 1966. This application Mar. 4, 1968, Ser. No. 711,163

Int. Cl. G01k /00; 301d 19/00; B04b 9/00 US. Cl. 731 15 Claims ABSTRACT OF THE DISCLOSURE An apparatus and method for removing gas from a column of mercury in a thermometer blank having a top chamber at the upper end thereof and a bulb at the lower end thereof. A constriction is located between the ends of the thermometer. A slug of mercury is located at the upper end and the column of mercury is located at the lower end below the constriction. The blank is spun about an axis intermediate its ends to force the mercury to the extremities of the blank and displace the gas which collects between the mercury located at the top end and the mercury at the bottom end of the thermometer so that when the column of mercury is heated the gas will be forced into the top chamber by the rising column of mercury from the bulb end. The blanks are mounted in a frame which is mounted on a shaft and both are driven by a drive means so that the frame and thermometers are spun about an axis which is located intermediate the ends of the blank.

Cross references to related application This application is a continuation-in-part of my earlier filed application Ser. No. 548,224, which was filed on May 6, 1966 and now abandoned.

Background of the invention It is well recognized that the presence of air or gas in a column of mercury in a thermometer blank is quite undesirable because the accuracy and reproducibility of any reading made on the thermometer would be affected. This woud be due partially to the compressibility and expandability of the entrapped gas. When a thermometer is heated or cooled the gas expands or compresses at a different rate than the mercury which results in the column of mercury rising or falling to an erroneous reading.

There exists a severe production problem in the manufacture of clinical thermometers. There is a stage of production where the majority of the air has been removed from a predetermined portion of mercury below the constriction of the capillary and an excess amount of mercury along with the majority of the previously entrapped gas are located above the constriction primarily in the top chamber at the end of the blank opposite to the bulb end. However, there may be a small amount of entrapped air remaining in the desired portion of mercury located in the blank below the constriction. At this point in production it is extremely difficult to get the remaining air out of this portion of mercury below the constriction without recombining it with the excess mercury and air already removed and located in the upper portion of the thermometer blank, which would thereby defeat the purpose of the operation. Therefore, if entrapped air is still remaining in the mercury below the constriction, the blank will never be able to be calibrated accurately enough to satisfy commercial thermometer standards. The blank becomes a reject and must be reworked or completely discarded. A significant and costly percentage of rejects of this type exist in the thermometer production art so that an improved method and apparatus for removing this remaining small amount of gas in the mercury below the constriction would be extremely desirable in the art. If this gas could be removed from the mercury below the constriction without recombining the already removed mercury and gas with the mercury below the constriction, then this remaining minute amount of gas can be driven off into the top chamber by later heating the mercury at the bulb end and pushing the gas ahead of the rising continuous mercury column into the top chamber Where the excess mercury and previously removed gas are. The thermometer blank is then ready for accurate calibration procedures according to well-known thermometer manufacturing methods. In this manner, the problem of the significant number of rejects of this type can be alleviated. Naturally, an economic apparatus and method for accomplishing this process quickly and efficiently so that a gas-free column of mercury remains in the blank, which may be accurately calibrated, would be extremely advantageous to the art.

Summary of the invention Therefore, the objectives of this invention include the provisions of an improved inexpensive centrifuging apparatus with which to remove gas from a predetermined column of mercury below the constriction in a thermometer blank both quickly and efliciently without removing the mercury from the blank and without recombining the mercury in the top chamber with the mercury below the constriction and in the bulb. It is also an objective of the invention to alleviate the above-mentioned problems existent in the thermometer manufacture art today so that an uninterrupted column of mercury is obtained below the constriction of the thermometer in order to promote accurate calibration of the thermometer blank during later steps of production. Furthermore, this invention provides an improved method of achieving the above discussed results whereby an uninterrupted gas-free column of mercury is obtained below the constriction in a thermometer blank in an economical and efficiently produced manner, and primarily to reduce the number of rejects due to the presence of difficult-to-remove small amounts of entrapped gas in a predetermined amount of mercury below the constriction within a thermometer blank.

An apparatus and method is provided for removing the gas from a column of mercury in a thermometer blank having a top chamber at its upper end and a bulb at its lower end. A constriction is located between the ends of the thermometer and a slug of mercury is located at the upper end while the column of mercury is located at the lower end below the constriction. The blank is spun about an axis intermediate its ends to force the mercury in opposite directions and into the extremities of the blank which thereby displaces the gas so that they be come located in the region between the opposite bodies of mercury. When the column of mercury is thereafter heated, the rising column from the bulb end of the blank will force the gas above it into the top chamber. The

blanks are mounted in a frame which is mounted on a shaft and both are driven by drive means so that the frame and thermometers are spun about an axis which is located intermediate the ends of the blank.

With the above and other objects in mind, reference is made to the attached drawings of the invention.

Brief description of the drawings In the drawings:

FIG. 1 is a side elevational view of centrifuging apparatus of the invention adapted to handle a plurality of thermometer blanks with part of the center portion broken away and removed;

FIG. 2 is an end elevation sectional view thereof taken along the plane of line 22 of FIG. 1 with a part of the center portion broken away and removed;

FIG. 3 is a top sectional plan View taken along the plane of line 33 in FIG. 1;

FIG. 4 is a front elevational view of an alternative embodiment of the invention in which individual thermometer blanks are handled, with the bottom portion of the support broken away;

FIG. 5 is a top plan view thereof; and

FIG. 6 is a side elevational view of the alternative embodiment with the bottom portion of both the support and the drive shaft broken away and removed.

Description of the preferred embodiments Referring now to the embodiments of FIGS. 1 through 3, the centrifuging apparatus 19 is shown in condition for operation with thermometer blanks 20 suitably mounted for entrapped gas removal from a column of mercury located below the constriction and near the bulb 26. The apparatus includes a drive shaft 21 which is suitably journaled and connected to a driving mechanism which may be of a conventional variety.

A frame 22 is suitably connected to or interposed on shaft 21 and rotates at the same speed and in the same direction. The frame 22 is essentially rectangular in configuration and has bracketed thereto a series of clips 23 arranged in two rows with each pair of opposed clips adapted to holding thermometer blank 20 during the spinning operation. In this connection, the thermometer blank 20 is held so that its longitudinal axis is substantially perpendicular to the spin axis of the shaft 21. The frame 22 is provided with strips 24 of resilient facing material. Strips 24 are somewhat resilient to serve to protect the ends of the thermometer 20 during the centrifugation operation and generation of centrifugal forces. Thus, facing material strips 24 form a cushion that will protect the thermometers from breakage during the spinning operation. As shown, the thermometer blanks 20 are preferably positioned so that their center of mass 25 is positioned proximate to the spin axis. However, proximity to the spin axis is not a necessity as long as the mercury below the constriction is thrust outwardly toward the bulb 26 and the mercury in the top chamber is thrust in the opposite direction. Consequently, displacement of the blanks laterally or longitudinally along the blank axis relative to the spin axis are contemplated by this invention, but the two masses of mercury are maintained on opposite sides of the spin axis.

In operating apparatus 19, shaft 21 and, consequently, frame 22 with its mounted thermometer blank 20 are rotated. By reason of centrifugal force, the heavier mercury in the thermometer blanks is forced radially outwardly toward bulbs 26 and toward top chambers 27. In this connection, it is contemplated that all or a major portion of the column of mercury we are principally concerned with will be below the construction of the thermometer blanks being handled prior to placement within apparatus 19. The gas we are concerned with is contained principally within this column of mercury be low the constriction and is the gas which is diflicult to remove which thereby cause the percentage of rejections as discussed above. Due to normal thermometer production techniques, there will also be a slug of previously removed mercury above the constriction and normally located in the blank at the point where the top chamber meets the bore of the thermometer bla-nk. Also, at this point in the manufacturing process, normally the majority of the gas will have already been removed from the thermometer blank and will be located above the constriction primarily in the top chamber above the slug of mercury. This is the condition of the blank when it is normally placed within the apparatus of this invention.

In operating the apparatus, the spinning of the blanks about a chosen axis forces the mercury below the constriction toward the bulb end of the thermometer blanks and the mercury in the top chamber in the opposite direction. Therefore, the mercury below the constriction displaces the remaining gas trapped within the column and forces this gas radially inward in the capillary bore toward the center of spin. When the desired degree of gas separation and displacement has occurred, rotation is stopped. The thermometer blanks may then be removed from the clips 23 and heated at the bulb end such that the column of mercury in bulb 26 and adjacent area below the constriction rises thereby pushing the displaced gas which has collected around the center of spin 25 ahead of the rising mercury column up into the top chamber portion 27 along with the slug of excess mercury. The heating is preferably done while the blanks are in an upright position with the bulbs at the bottom. Top chamber 27 is subsequently removed during the manufacturing process thereby removing the gas within the thermometer blank. Consequently, a gas-free column of mercury within the capillary bore of the thermometer blank is achieved. The thermometer blank may then be accurately calibrated and inaccurate reading due to the compressibility or expandability of the entrapped gas in the mercury column is, therefore, eliminated. Furthermore, the number of rejects due to the presence of gas entrapped in the column of mercury below the constriction is greatly reduced since this gas may now be removed by the use of centrifugal force whereby the thermometer is spun about an axis between its ends so that the previously removed gas and excess mercury above the constriction is not recombined with the column of mercury below the constriction.

We refer now to the alternative embodiment of this invention depicted in FIGS. 4 through 6. Drive shaft 30 has suitably keyed thereto a rubber-faced wheel 31 forming part of a friction type drive for the wheel 32. Wheel 32 is connected to one end of shaft 33 which is connected to frame 34 which is journaled in a support 35. Thrust bearing 36 is between the interface of wheel 32 and support 35 so that when the friction drive wheel 31 forces the wheel 32 to rotate, it will rotate smoothly and easily in relation to support 35.

Two clips 37 are located on the face of the frame and are aligned so that together they will hold a thermometer blank 38 in a substantially fixed position with its center of mass 39 preferably coincidental with the center of rotation of the frame.

A pair of diametrically opposed threaded studs 42 extend from frame 34. Knurled adjustable circular end stops 43 are threaded on studs 42. These end stops 43 cooperate in holding the thermometer blank 38 and preventing it from sliding free of the two clips 37 under the action of centrifugal force. In order to minimize the danger of breakage of the thermometer 38, the inner faces of the end stops 43 are composed of a resilient material 44.

In operation, the shaft 30 is rotated by drive means which rotates wheel 31 and consequently wheel 32. The shaft 33 is, accordingly, rotated to spin frame 34 and all of its attachments, including the thermometer blank being held by the two clips 37. The induced centrifugal forces force the heavier mercury column Within the capillary bore below the constriction of thermometer blank 38 radially outwardly into bulb 40. Similarly the slug of excess mercury within thermometer blank 38 in the top chamber is forced outwardly away from the spin axis. The gas is displaced by the mercury and forced between the slug of excess mercury and the column of mercury in the bulb end. For best results, in this embodiment and in the previously mentioned embodiment, the center of spin is preferably located between the constriction and the end of the thermometer distal from the bulb end.

As in the previously discussed embodiments, rotation is eventually stopped and the thermometer blank is removed and the bulb heated in an upright position. The column of mercury below the constriction rises and drives the gas up into the top chamber 41 along with the previously located slug of excess mercury. Top chamber 41 is subsequently removed during the manufacturing process. The resultant column of mercury within the thermometer blank is virtually free from any gas trapped within which could aifect the eventual accuracy of the thermometer after calibration and marking according to standard techniques. Thus, all of the significant amounts of entrapped gas in the column of mercury are removed and, therefore, the significant number of rejected thermometers due to this problem is greatly decreased.

Thus, an improved apparatus and method are provided for alleviating the problem of rejection of thermometer blanks during manufacture due to the presence of a significant amount of entrapped gas in the column of mercury below the constriction after the majority of gas and an excess amount of mercury have been removed therefrom and are located in the upper portion of the thermometer blank adjacent to or in the top chamber thereof. The improved apparatus and method of this invention involves low production cost, is efficient and is capable of adaption to mass production techniques.

Thus, the above-mentioned objects of the invention, among others, are achieved. The range and scope of the invention are defined in the appended claims.

I claim:

1. An apparatus for removing gas from a column of mercury in a thermometer blank having a top chamber at the upper end thereof and a bulb at the lower end thereof with a constriction therebetween and having a slug of mercury at the upper end and the column of mercury at the lower end below the constriction comprising:

a rotatable shaft coupled with a drive means;

a frame connected to said shaft so as to spin as the shaft rotates;

holding devices connected to the spinning frame;

said holding devices positioned so as to hold at least one thermometer blank so that the axis about which the thermometer blank spin is located intermediate its ends so that the mercury at one side of the axis is driven toward the top chamber and the mercury at the opposite side of the axis is driven toward the bulb under the influence of centrifugal forces with gas in the blank collecting between the two bodies of mercury at the extremities;

restraining means for cooperating in restraining the blank within the holding devices during spinning thereof; and means to remove the separated gas.

2. The invention in accordance with claim =1 wherein the frame is connected intermediate the ends of the rotating shaft and is approximately rectangular in shape.

3. The invention in accordance with claim 2 wherein said holding devices are clips arranged in pairs fastened to the frame, each pair of said clips are aligned so as to hold a thermometer blank in the required position.

4. The invention in accordance with claim 2 wherein said restraining means are strips of resilient facing material positioned and fastened on surfaces of the frame and in aligned relationship with the ends of the held thermometer blanks, in order that said thermometer blanks are prevented from sliding longitudinally out of said holding devices, said restraining means being of resilient material for minimizing breakage.

5. The invention in accordance with claim 1 wherein a rubber-faced wheel is coupled with the drive means, a second wheel coupled with the rotatable shaft, said rubberfaced wheel contacts and by reason of friction, drives said second wheel, a fixed support, said shaft is journaled in said fixed support, and thrust bearings interposed between said fixed support and said second wheel for facilitating the rotation of said second turning wheel relative to said fixed support.

6. The invention in accordance with claim '1 wherein said frame has a longitudinal axis perpendicular to the axis of the rotating shaft and is connected to one end of said shaft, the other end of said shaft being connected to a drive means, and said shaft being connected to said spinning frame at approximately the center of said frame.

7. The invention in accordance with claim 6 wherein said holding devices ihcludes a pair of clips for holding a thermometer blank so that its center of mass is in a predetermined position.

8. The invention in accordance with claim 6 wherein said restraining means includes threaded studs extending from opposed ends of the frame in approximate alignment with the longitudinal axis of the frame, knurled adjustable end stops threaded on said studs and positioned approximately normal to the axis of said thermometer blank held by the holding device and having surfaces aligned therewith to cooperate in preventing the held thermometer blank from sliding longitudinally out of the holding devices.

9. The invention in accordance with claim 8 wherein the interface of each said knurled adjustable end stop is covered with resilient facing material adapted to be engaged by the end of the held thermometer blank in order to prevent breakage of said thermometer blank when it contacts said end stops and is restrained from sliding out of said holding devices.

10. The invention in accordance with claim 1 wherein the said holding devices are positioned so as to hold at least one thermometer blank such that the axis about which the thermometer blank is adapted to spin is located between the constriction and the end of the blank at which the top chamber is located.

11. The invention in accordance with claim 1 wherein the said holding devices are positioned so as to hold at least one thermometer blank such that the axis about which the thermometer blank is adapted to spin is located approximately coincidental with the center of mass of the blank.

12. A method for removing the gas from a column of mercury in a thermometer blank having a top chamber at the upper end thereof and a bulb at the lower end thereof with a constriction therebetween and having a slug of mercury at the upper end and the column of mercury at the lower end below the constriction comprrsrng:

spinning the blank about an axis located between the ends thereof to force the mercury below the spin axis toward the bulb and the mercury above the axis toward the top chamber under the influence of centrifugal force with the gas in the blank collecting between the mercury in the bulb and the mercury in the top chamber;

heating the blank to cause the mercury column to rise and force the above gas into the top chamber; and

subsequently removing the top chamber to provide a 7 column of mercury with no entrapped gas in the thermometer blank.

13. The invention in accordance with claim 12 wherein the thermometer blank is spun about an axis located between the constriction and the end of the blank at which the top chamber is located.

14. The invention in accordance with claim 12 wherein the thermometer blank is spun about an axis located approximately coincidental with its center of mass.

15. The invention in accordance with claim 12 wherein the thermometer containing the uninterrupted column of mercury is then calibrated and marked.

References Cited UNITED STATES PATENTS 2,160,280 5/1939 Persons 233-26 2,179,839 11/1939 Brosnan 233-26 2,685,799 8/1954 Sullivan 73-373 3,289,927 12/ 1966 Nelson 233-26 REUBEN FRIEDMAN, Primary Examiner C. N. HART, Assistant Examiner US. Cl. X.R. 29-400, 422; 55-52, 199; 141-11, 69; 233-26 

